JP5883861B2 - Method for producing organic semiconductor layer comprising mixture of first and second semiconductors - Google Patents

Description

  The present invention relates to the manufacture of an organic semiconductor layer formed from a mixture of first and second semiconductor materials, more specifically an organic semiconductor layer involved in the formation of an organic optoelectronic device, particularly a photodiode.

  Referring to FIG. 1, this is a simplified cross-sectional view of a prior art organic photodiode 10, which is typically referred to as a transparent substrate 12 made of, for example, glass and, for example, “ITO”. A layer 14 forming a first electrode formed from indium tin oxide, for example poly (3,4-ethylenedioxythiophene) commonly referred to as “PEDOT”, and polystyrene sulfone generally referred to as “PSS” Formed from a mixture of sodium acids, such mixture itself is an injection layer 16, usually called “PEDOT: PSS”, which facilitates the transfer of holes from the first electrode 14 to the active semiconductor layer 18. 16 and a mixture of two organic semiconductor materials P and N, usually a mixture of two polymers, eg commonly referred to as “P3HT” Active semiconductor layer 18 forming a PN junction formed from a mixture of poly (3-hexylthiophene) and [6,6] phenyl C61 butyric acid methyl ester, commonly referred to as “PCBM”, for example calcium, silver Or a bottom-to-top stack formed from a layer 20 that forms a second electrode that is made of aluminum and that favors calcium because of the low work function that can collect only electrons.

  In operation, electromagnetic radiation irradiates the substrate 12, and photons that reach the active layer 18 generate electron-hole pairs. By applying a potential difference to electrodes 14 and 20 with a value that depends on the illumination of photodiode 10, current is then collected.

  However, the efficiency of the photodiode 10 depends on the contact area existing in the active layer 18 between the P-type organic semiconductor material, for example, P3HT, and the N-type organic semiconductor material, for example, PCBM. The efficiency decreases rapidly with it. Furthermore, the efficiency also depends on the size of the region, and the expansion of the region must be small so that the charges can cross them and reach the electrode without recombination. Therefore, the active layer 18 that is ideal in this respect is formed by a mixture of two organic semiconductor materials that is uniform on a molecular scale.

  However, this uniformity cannot be achieved with current deposition techniques. In practice, the active layer 18 is usually formed by deposition of a solution containing a solvent having an organic semiconductor material dissolved or dispersed therein, and subsequent evaporation of the solvent.

  If the solvent evaporation rate is too low, then phase separation may be observed, and finally the layer 18 is formed from the layer 22 of the first semiconductor material and the layer 24 of the second semiconductor material. Therefore, the contact surface 26 between the two materials is very small and the efficiency of the photodiode 10 is reduced.

  As shown in FIGS. 2A-2D, this problem also occurs when a highly volatile solvent such as toluene is selected. Thus, when the two semiconductor materials are mixed in toluene (FIG. 2A), for example by magnetic stirring, in order to form a mixture that is as homogeneous as possible initially, the resulting solution is very unstable. Local phase separation (FIG. 2B) due to thermodynamic factors, and from physicochemical attraction and repulsion between molecules, appears rapidly even before the solution is deposited on the first electrode 14 (FIG. FIG. 2C). This phenomenon continues as the volatile solvent evaporates, and large areas formed from a single type of material can eventually be observed in layer 18.

  Thus, it can usually be observed that 80% of the region has at least one dimension greater than 10 μm. Thus, the total contact area between the two organic semiconductor materials is again reduced here and the efficiency of the photodiode is low.

  Patent Document 1 describes a method for producing an organic semiconductor layer including a porous body made from a first semiconductor material having pores filled with a second semiconductor material. The porous body is produced by using phase separation of two materials mixed in solution, after which the second material is removed to clean the lateral holes after the solution has solidified. First of all, it is difficult to accurately set the pore shape and particularly the dimensions by such a method for producing a porous body, and the residue of the second material remains, which adversely affects the quality of the organic semiconductor layer. .

US Patent Application Publication No. 2009/050206

  The present invention is formed by two organic semiconductor materials having a porous body made from a first semiconductor material having a large contact area between these materials, ie, pores at least partially impregnated with a second semiconductor material. An object of the present invention is to solve the above-mentioned problems by providing a method for manufacturing an organic semiconductor layer. This makes it possible to improve the fixing of the pore shape and to obtain a porous body free of residues that can adversely affect the quality of the organic semiconductor layer.

  To achieve this, a method for manufacturing such a layer comprises the formation of a porous solid volume formed from a first semiconductor material with an effective porosity that can accept a second semiconductor material, and a first semiconductor material On the outer surface of at least the porous solid volume of a liquid that is inert to the liquid and that has an evaporation temperature below the evaporation temperature of the second semiconductor material, the liquid containing the second semiconductor material dissolved or dispersed in the solvent And evaporation of the solvent by heating the porous solid volume at least partially once with the liquid and heating at a temperature above the evaporation temperature of the solvent and below the evaporation temperature of the first and second semiconductor materials; including.

Formation of the porous liquid includes the introduction of bubbles into the solution of the first semiconductor material dissolved or dispersed in the solvent and the subsequent evaporation of the solvent, where the solvent temperature is less than the gas evaporation temperature. .

“Effective porosity” as used herein refers to a material having pores that are accessible from the outside and thus can be “filled”, which can be passed back and forth to form a space inside the material.

  In other words, a stable and large contact area is created before the two organic materials are placed in contact. And this surface area is independent of the lack of physicochemical affinity of the two semiconductor materials, resulting in a very uniform semiconductor layer with improved bonding between the two semiconductor materials. For example, a significant increase in the efficiency of the organic photodiode can be observed in the range of 5 to 100 times.

  Thereafter, the production of porous solid volumes makes it possible on the one hand to obtain a great variety of pore sizes and densities and on the other hand to form “clean” materials without residue.

  In fact, the use of gas makes it possible to obtain smaller bubbles than droplets that can be obtained from an emulsion of one or more materials in a solvent, thus forming very fine pores and thus a porous body. It is possible to have high-density pores that are uniformly distributed over the entire volume of the first material. Furthermore, depending on the gas selected, the bubble size is variable, and the pore diameter can be adjusted more accurately.

  Furthermore, gas evaporation does not leave a residue in the final porous solid volume.

  According to an embodiment of the present invention, the first semiconductor material is P3HT and the second semiconductor material is PCBM.

  The present invention is also directed to an optoelectronic device comprising a semiconductor layer formed by the method described above and disposed between first and second electrodes.

FIG. 2 is a simplified cross-sectional view of a prior art organic photodiode. 2 illustrates a prior art method for depositing a solution comprising two organic semiconductor materials in a volatile solvent to form an active layer of a prior art organic photodiode. FIG. 2 shows a simplified cross-sectional view at various stages of a method of manufacturing an organic photodiode according to the present invention. FIG. 2 shows a simplified cross-sectional view at various stages of a method of manufacturing an organic photodiode according to the present invention. FIG. 2 shows a simplified cross-sectional view at various stages of a method of manufacturing an organic photodiode according to the present invention. FIG. 2 shows a simplified cross-sectional view at various stages of a method of manufacturing an organic photodiode according to the present invention. FIG. 2 shows a simplified cross-sectional view at various stages of a method of manufacturing an organic photodiode according to the present invention. FIG. 2 shows a simplified cross-sectional view at various stages of a method of manufacturing an organic photodiode according to the present invention. FIG. 2 shows a simplified cross-sectional view at various stages of a method of manufacturing an organic photodiode according to the present invention.

  The invention will be better understood upon reading the following description, given by way of example only, in conjunction with the accompanying figures, in which: Here, the same reference signs refer to the same or similar elements.

  Referring to FIGS. 3A to 3G, the method of manufacturing an organic photodiode according to the present invention usually starts with the formation of a glass substrate 12 (FIG. 3A), on the substrate 12 to form the first electrode of the photodiode. This is followed by the formation of metallized ITO (14) by etching with (FIG. 3B). Thereafter, in this method, the deposition of the PEDOT: PSS injection layer 16 is usually continued on the first electrode 14 (FIG. 3C).

  The method continues with the production of a porous P3HT layer. More specifically, P3HT is dissolved or dispersed in a first solvent “B” such as an alkane. The solution thus obtained is immiscible with the first solvent “B” and is mixed with the second solvent “C” which has a lower evaporation temperature than the first solvent “B”. For example, the first solvent is chlorobenzene or chloroform. The mixture thus obtained is emulsified, for example by mechanical stirring, and the emulsion 30 is deposited on the injection layer 16 (FIG. 3D).

  Thereafter, the second solvent “C” evaporates by being heated at a temperature that is equal to or higher than its own evaporation temperature but lower than the evaporation temperature of the first solvent “B”. Thereafter, the first solvent “B” evaporates by being heated at a temperature higher than its own evaporation temperature, for example.

A P3HT porous solid layer 32 having an open porosity that can accept a PCBM solution is thus obtained (FIG. 3E). Layer 32 has pores with a diameter of 100 nm with a (linear) distribution with a total surface area of more than 500 μm ² and 10 pores / μm.

  The characteristics of the emulsion, and in particular the size of the P3HT droplets in the first solvent B and the concentration of the droplets in the second solvent C, determine the final porosity of the porous layer 32. It is thus possible to form a layer 32 comprising macropores having a width greater than 50 nm, mesopores having a width of 2 nm to 50 nm, or micropores having a width of less than 2 nm. The pore size is determined by the nature of the solvent, by their degree of immiscibility and by their evaporation rate.

  Advantageously, additives may also be added to stabilize the aforementioned emulsions, especially when the droplets are highly concentrated. For example, the additive is a surfactant, eg, a polymer that is an emulsifier such as a biopolymer, such as soap microparticles, or a hydrophilic amine polymer such as aminotrimethoxysilane.

  Furthermore, in the presence of a surfactant, the emulsifier has the advantage of lowering the interfacial tension between the two solvents to a few mN / m, or even a few μN / m, and provides the necessary force to increase the interfacial area. It is possible to decrease. This maintains a small domain size and increases porosity.

  The method then continues by depositing a PCBM solution 34 in a third solvent “A”, eg, cyclohexane, on the free surface of the porous layer 32. The solution is then completely impregnated with the porous layer 32 (FIG. 3F).

  The third solvent “A” used to dissolve or disperse PCBM is selected to have a lower evaporation temperature than PCBM and is preferably volatile. The solvent is selected to be inert to the material forming the porous layer 32, in this case P3HT, to avoid dissolving the material in reverse.

  Thereafter, heating of the porous layer 32 impregnated with the PCBM solution is performed at a temperature equal to or higher than the evaporation temperature of the third solvent but lower than the evaporation temperature of PCBM. An organic semiconductor layer 38 formed from a mixture of P3HT and PCBM with a high degree of uniformity is thus obtained (FIG. 3G).

  The method is then terminated by depositing on the free surface of layer 38 a layer 20 forming a second electrode, for example a layer of calcium, aluminum or silver.

  The aforementioned porous layer is obtained by emulsion.

  As a variant, the porous layer is obtained by polymerization of polystyrene. Porous polystyrene with porosity obtained directly during the polymerization is used. The polystyrene pores are filled first with the first material and then with the second material. Thereafter, the polystyrene remains as an inert framework.

  According to the invention, the porous layer is obtained by adding gas, ie by forming bubbles. Bubbles are introduced into the solution containing the first material. During evaporation of the solvent, if the evaporation temperature of the solvent is below the vaporization temperature of the gas, then the bubbles remain trapped. Thus the solvent evaporates as the gas is released. The latter can be artificially introduced (air, carbon dioxide) or generated in situ by polymerization of a first material that produces a residue (carbon dioxide), such as polymerization of polyurethane or epoxy resin, for example.

  The size of the bubbles and the nature of the gas make it possible to accurately set the shape of the pores, especially their size and density.

  Similarly, embodiments have been described in which a porous P3HT layer is filled with PCBM. As a variant, a porous PCBM layer is filled with P3HT.

  Similarly, embodiments have been described where P3HT and PCBM are used. Of course, other types of polymer or non-polymeric organic semiconductor materials can be used depending on the intended application. The choice of the first and second solvents used to form the emulsion that provides the active organic layer after removal of the emulsion is clearly dependent on the choice of the organic semiconductor material. The only thing to note is that the solvent is chosen to be immiscible or very slightly miscible together and that the evaporation temperature of the second solvent is below the evaporation temperature of the first solvent.

  Similarly, embodiments in which organic photodiodes are manufactured have been described. Of course, the organic semiconductor layer formed from the mixture of semiconductor materials obtained by the manufacturing method according to the invention can be used in other types of organic microelectronic components, for example bipolar transistors.

DESCRIPTION OF SYMBOLS 10 Photodiode 12 Transparent substrate 14 1st electrode 16 Injection layer 18 Active layer 20 2nd electrode 22 Layer of 1st semiconductor material 24 Layer of 2nd semiconductor material 26 Contact surface 30 Emulsion 32 Porous layer 34 PCBM solution 38 Organic semiconductor layer

Claims (2)

A method for producing an organic semiconductor layer (38) formed from a mixture of first and second organic semiconductor materials, comprising:
Forming a porous solid volume (32) formed from the first semiconductor material that has an effective porosity and is capable of receiving the second semiconductor material;
A liquid (32) comprising the second semiconductor material dissolved or dispersed in a solvent (A) that is inert to the first semiconductor material and has an evaporation temperature less than the evaporation temperature of the second semiconductor material. Depositing at least on the outer surface of the porous solid volume;
As soon as the porous solid volume (32) is at least partially impregnated with the liquid, it is heated to a temperature above the evaporation temperature of the solvent and below the evaporation temperature of the first and second semiconductor materials. Evaporating the solvent (A)
Wherein formation of the porous solid volume, the step of adding a gas for introducing gas bubbles into the solution of the first semiconductor material dissolved or dispersed in Solvent, and steps of evaporating followed the Solvent the method, wherein the evaporation temperature of the solvent medium is lower than the evaporation temperature of the gas for introducing gas bubbles into the solution of the first semiconductor material.   The method of claim 1, wherein the first semiconductor material is P3HT and the second semiconductor material is PCBM.

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